IMDb Goof

I believe that's because Kuttner didn't actually write the novelization. From what I have heard, a minor author of the time wrote the novelization, and the studio somehow credited it to Kuttner--probably as a way to lure people to buy the book and watch the movie.

I own the book Dr. Cyclops which is by Henry Kuttner--and which contains other Kuttner stories. The title story is listed as being published in 1940, the same year as the film. The Encyclopedia of Science Fiction terms the published story as a "novelization" by Will Garth, stating that it "was probably the work of Alexander Salalman." That assumption appears to be incorrect. The most likely final answer is that--unbeknownst to the Encyclopedia of SF writer--Kuttner wrote the published story, based on the film, rather than having written an original upon which the film was based. As such, Kuttner's name does not belong on the IMDB writers' credits.